1. Field of the Invention
Compounds which are phosphorus esters wherein such compounds contain one to three 1,3,2-dioxophosphorinane rings. The compounds within the scope of this invention are also flame retardants for polyurethane and polystyrene polymeric compositions.
2. Description of the Prior Art
During the past several years, a large number of flame retardants have been developed for use with an almost equally large number of flammable materials. Cellulosic materials such as paper and wood and polymeric materials such polyolefins, polyurethane, and polystyrene are just two examples of materials for which flame retardants have been developed. For any class of flammable materials, such as synthetic type polymers, those skilled in the art have long been aware that some flame retardant additives are more effective in polymers and polymeric compositions than other flame retardant additives. This is because the efficacy of any flame retardant in polymers or polymeric compositions is measured not only by the flame retardant capability of the additive but also by the ability of the additive to improve or modify, or at least not to detract from, other physical or mechanical properties of the polymer or polymeric composition. The mere fact, therefore, that most flame retardants contain halogen and phosphorus atoms does not assure that any given halogenated or phosphorus-containing compound will impart usable flame retarding charcteristics to all or even to any polymeric system. Furthermore, as those skilled in the art have improved the flame retardancy of many polymeric materials, they have been simultaneously required to provide the necessary flame retardancy with a minimal effect upon other properties of the polymer such as the light stability, processability, and flexural, tensile and impact strengths. Also, it has been the desire of those involved in the art of flame retardants to provide flame retardants having a durable lasting effect. Balancing all of the foregoing considerations and thereby developing polymeric compositions with good flame retardant characteristics as well as a satisfactory balance of other properties is, consequently, a task which has in the past and presently continues to require the exercise of a high degree of inventive skill.
In particular, U.S. Pat. No. 3,784,592 discloses that three moles of dibromoneopentyl glycol can be reacted with one mole of phosphorus oxychloride to produce tris(2,2-bis(bromomethyl)-3-propanol)phosphate, a compound having a structure very different from the novel reactive flame retardant compounds of this invention.
U.S. Pat. No. 2,952,701 (hereinafter referred to as McConnell et al.) discloses, inter alia, compounds of the formula: ##STR2## wherein G is selected from the group consisting of oxygen and sulfur. The organophosphorus compounds within the scope of McConnell et al. are useful as flame-proofing plasticizers, stabilizers, synthetic lubricants, force transmission fluids, lubricating oil additives, pesticides, and intermediates for the preparation of other organophosphorus compounds.
U.S. Pat. No. 3,890,409 (hereinafter referred to as Mayerhoefer et al.) disclose compounds of the formula: ##STR3## wherein R.sub.1 and R.sub.2 are each, independently, hydrogen or alkyl of 1 to 5 carbon atoms, and n, inter alia, may be 1 and Y can be, inter alia, ##STR4## wherein each X is, independently, chlorine or bromine and Z is alkyl of 1 to 4 carbon atoms or EQU --CH.sub.2 X
wherein X is as defined above, and m is zero or the integer 1. Mayerhoefer et al. disclose that their compounds are useful flame retardants.
German 2,262,336 (hereinafter referred to as Shim) discloses flame retardant halogenated neopentylglycol-monophosphate and diphosphate esters of the formulas: ##STR5## wherein R represents, inter alia, C.sub.1 to C.sub.10 alkyl-, a C.sub.1 to C.sub.10 halogenalkyl-, and a C.sub.1 to C.sub.10 hydroxyalkyl-. X represents halogen such as preferably bromine, while R is preferably, inter alia, a C.sub.1 to C.sub.4 haloalkyl-. Y is either oxygen or sulfur, preferably oxygen.
Neither McConnell et al. nor Mayerhoefer et al. nor Shim disclose that their respective compounds can contain methylol substitutes attached to the 2' carbon atom. As those skilled in the art of flame retardants know, the indiscriminate substitution of a hydroxyl group for a halogen or hydrogen atom of a compound will result in a dramatic decrease in the modified hydroxy substituted compound's hydrolytic and thermal stability. However, by the use of a high degree of inventive skill, it is possible to effectuate a substitution of a hydroxyl group for a halogen or hydrogen atom and still maintain the basic physical properties of the nonhydroxyl-containing compound. The net result of this inventive skill is that one is thereby able to produce a reactive flame retardant capable of reactively being bound into a polymer chain, e.g., polyurethane and polyester, and thereby reducing the migration of the flame retardant and the subsequent flame retardancy loss of the polymeric composition. This result has long been sought after and much desired in the art of flame retardants.